1. Technical Field
This invention relates generally to an apparatus and method for analyzing a fluid sample, and, more particularly, to a self-contained analyzer for on-site use and analysis.
2. Discussion of the Related Art
There has been much interest and investigation into apparatus and methods for obtaining accurate analysis of lubricating oils (used and fresh) as well as functional fluids. The term xe2x80x9cfunctional fluidsxe2x80x9d relates to liquid materials used in mechanical equipment, and which may be or may perform primarily lubrication and/or power transmission functions (e.g., gearbox oils, automatic transmission fluid, machine oils and hydraulic fluids or oils, etc.). xe2x80x9cFunctional fluidsxe2x80x9d also includes coolants, thermal transmission media, and fuels. The reasons for such interest include, but are not limited to, (i) the assessment of the constituent, condition and quality of the oil/fluid, (ii) the condition of the equipment from which the oil/fluid was drawn, and (iii) the condition of components of such equipment.
As is known, oil is generally used to lubricate moving parts in mechanical systems, such as engines, transmissions, hydraulics and vehicles. Certain substances, referred to generally as contaminants, are not originally present in the oil but rather are produced as the by-products of wear and corrosion. For example, metal particulates may be formed through abrasion or chemical corrosion and cause further deterioration of internal parts. In addition, normal operation causes oxidation, nitration and sulfation of the oil, altering a desired chemistry thereof. Further, leaks between the cooling systems and the lubricating system may cause coolant (mixtures of water, ethylene glycol and other coolant chemicals) to be introduced into the oil.
Lubricant oil filters are designed to remove the larger size particulates from oil. However, this gross filtering nonetheless leaves the majority of smaller contaminants free to further affect the equipment. For example, non-metallic components, such as pump diaphragms, gaskets and seals, fluid lines and the like, may be further affected. Moreover, contaminants in the oil, such as ethylene glycol, fuel, silicone, water, soot and other chemicals may also present concerns.
Historically, accurate oil analysis has been provided mainly in a laboratory setting, such as, for example, a system utilized in a laboratory as disclosed in U.S. Pat. No. 3,526,127 issued to Sarkis on Sep. 1, 1970.
One approach to accurate on-site oil analysis was to provide a self-contained test assembly in a single housing, as described in U.S. Pat. Nos. 5,517,427 and 5,537,336, both issued to Joyce (the xe2x80x9cJoyce patentsxe2x80x9d), both hereby expressly incorporated by reference in its entirety. The Joyce patents disclose a test assembly that includes an infrared (IR) spectrometer and an optical emission spectrometer for producing a report on the amount of certain metals in an oil sample, other oil contaminants such as water, glycol, soot, etc. as well as oil condition. With respect to the optical emission spectrometer portion, the Joyce patents disclose the use of xe2x80x9cphotocellsxe2x80x9d (the commercial embodiment corresponding to the Joyce patents employed well-known photo multiplier tubes (PMT)) to optically monitor spark induced light emissions of the oil sample to determine wear metals content.
Although PMTs in the manner configured (i.e., incorporated into a large monochromator in the commercial embodiment corresponding to the Joyce patents) provide xe2x80x9chigh resolutionxe2x80x9d, such a configurations presents certain constraints. First, inherent in such systems are certain geometric and mechanical constraints imposed by the physical dimensions of a PMT. Since each PMT was configured to monitor a fixed wavelength, the system had to be made relatively, physically large to ensure that light from multiple wavelengths would not impinge on the same PMT. Second, the configuration provided little if any flexibility in emission line selection/reconfiguration. Finally, as the number of monitored emission lines increased, so would the corresponding cost (due to the required addition of another PMT). Thus, while the apparatus disclosed in the Joyce patents provided satisfactory performance, it would be desirable to provide an apparatus having a reduced size, weight and cost.
In addition, it is known to conduct spark emission spectroscopy in a commercial lab setting. It is further known to use carbon electrodes inasmuch as carbon material has relatively few emission lines that interfere with the spectral measurements. However, a problem with carbon electrodes is that they wear relatively quickly, and so must be frequently replaced. Continual replacement of electrodes for spark emission spectrometers deployed for long-term on-site operation, however, is all but impractical. It is also known that to ensure instrumental repeatability, the electrodes spark surfaces should be maintained parallel and spaced apart with a constant gap from measurement to measurement.
In view of the foregoing, one approach has been to use relatively durable electrodes, such as electrodes comprising silver material, as seen by reference to U.S. Pat. No. 5,610,706 entitled xe2x80x9cANALYSIS SYSTEMxe2x80x9d issued to Carroll et al. Carroll et al. disclose a spark emission spectrometer for analyzing used engine lubricating oil wherein the system includes a pair of vertically opposed electrodes enclosed in a chamber, the respective faces of the electrodes opposing each other, i.e., one above the other with the spark surfaces generally parallel, and spaced apart a predetermined distance. Carroll et al. further disclose a chamber having an access door in a front wall of the chamber, an exhaust port in a rear wall of the chamber, and an exhaust fan coupled to the exhaust port for exhausting air from the chamber.
A potential problem with the durable, metal, electrodes is that sparking causes wear of the electrodes by ablating metal at the hot electrodes surface. Moreover, a particular, known problem is that the wear may be uneven, producing a wedge angle between the electrodes, compromising the optimal configuration needed for instrumental repeatability (i.e., parallel spark surfaces spaced apart with a constant gap).
Accordingly, there is a need to provide an improved apparatus for analysis of a fluid sample that minimizes or eliminates one or more of the problems as set forth above.
In one aspect of the invention, an apparatus for analyzing a fluid sample is provided which has the advantage of even-wearing spark electrodes. Even-wearing electrodes improves instrumental repeatability, providing improved measurements. Elimination of the xe2x80x9cwedge anglexe2x80x9d wear profile improves operation of the apparatus. Even-wearing is achieved by constraining airflow in the spark stand enclosure to substantially laminar airflow, which travels in a direction parallel to the body of the generally cylindrical shaped upper and lower spark electrodes (i.e., substantially perpendicular to the respective spark surfaces of the upper and lower electrodes).
An apparatus for analyzing a fluid sample in accordance with the present invention includes an enclosure, upper and lower electrodes, a fluid transfer assembly, a spectrometer assembly, a computer controller, and an exhaust assembly. The enclosure has an open position and a closed position. The upper and lower electrodes are disposed in the enclosure, and the electrodes are generally disposed along a longitudinal axis (xe2x80x9cAxe2x80x9d). Each electrode has a respective spark surface associated therewith. The spark surfaces are spaced apart to define a gap region therebetween. The electrodes are configured to be connected to a power supply for causing an electric discharge across the gap region for exciting the fluid sample to spectroemissive levels. The fluid transfer assembly is configured to deliver the fluid sample to the gap region. The spectrometer assembly is disposed in sensing relation with the gap region and is configured to sense the spectroemissive levels and generate spectral data in response thereto. The computer controller is configured to generate an output in response to the spectral data and a predetermined operating strategy. The exhaust assembly is coupled to the enclosure and is configured to exhaust an interior volume of the enclosure.
In accordance with the invention, the enclosure includes an airflow passage having a first region characterized by airflow that is substantially parallel to the longitudinal axis when the exhaust assembly is operated and the enclosure is in the closed position. The spark surfaces are contained in the first region whereby the spark electrodes wear evenly improving spectral measurements.